Aws-load-balancer-controller: Create security group if annotation is not provided

[mgoodness]

If alb.ingress.kubernetes.io/security-groups is not specified, we should create an appropriate security group. This would mirror the behavior of Service type: LoadBalancer on AWS.

[tavisma]

+1

[justinclayton]

Other ingress controllers have established a pattern of using a ConfigMap for global defaults. Here is an example of how the nginx controller does it. I'd love it if this project followed this pattern.

[greg-jaunt]

Beyond just creating the security group, the alb-ingress-controller needs to assign the security group to the instance nodes.

[joshrosso]

I'm going to add this to 1.0, it'll make our examples easier.

[joshrosso]

Added, docs coming soon as part of #197